A varied AvrXa23-like TALE enables the bacterial blight pathogen to avoid being trapped by Xa23 resistance gene in rice

Zhengyin Xu; Xiameng Xu; Yijie Wang; Linlin Liu; Ying Li; Yangyang Yang; Liang Liu; Lifang Zou; Gongyou Chen

doi:10.1016/j.jare.2022.01.007

A varied AvrXa23-like TALE enables the bacterial blight pathogen to avoid being trapped by Xa23 resistance gene in rice

J Adv Res. 2022 Dec:42:263-272. doi: 10.1016/j.jare.2022.01.007. Epub 2022 Jan 29.

Authors

Zhengyin Xu¹, Xiameng Xu¹, Yijie Wang², Linlin Liu¹, Ying Li¹, Yangyang Yang², Liang Liu², Lifang Zou¹, Gongyou Chen³

Affiliations

¹ Shanghai Collaborative Innovation Center of Agri-Seeds/School of Agriculture and Biology, Shanghai Jiao Tong University, Shanghai 200240, China; State Key Laboratory of Microbial Metabolism, Shanghai Jiao Tong University, Shanghai 200240, China.
² Shanghai Collaborative Innovation Center of Agri-Seeds/School of Agriculture and Biology, Shanghai Jiao Tong University, Shanghai 200240, China.
³ Shanghai Collaborative Innovation Center of Agri-Seeds/School of Agriculture and Biology, Shanghai Jiao Tong University, Shanghai 200240, China; State Key Laboratory of Microbial Metabolism, Shanghai Jiao Tong University, Shanghai 200240, China. Electronic address: gyouchen@sjtu.edu.cn.

Abstract

Introduction: Xa23 as an executor mediates broad-spectrum resistance to Xanthomonas oryzae pv. oryzae (Xoo), which contains a matching avirulence gene avrXa23, in rice for bacterial leaf blight (BLB). avrXa23 encodes a transcription activator-like effector (TALE) protein which binds to the EBE (effector-binding element) of the Xa23 promoter. It is unclear whether the considerable pressure of Xa23 leads to an emerging Xoo strain that overcomes Xa23 resistance.

Objectives: This study aimed to uncover new Xoo isolate(s) that overcome Xa23-mediated resistance and to investigate how the pathogen evades the resistance.

Methods: Totally 185 Xoo isolates were used to screen possibly compatible strain(s) with Xa23-containing rice CBB23 by pathogenicity test. Genome Sequencing, Southern blot, tal gene cloning, Western blot, qRT-PCR and electrophoretic mobility shift assays (EMSA) were conducted to determine the mechanism of one Xoo isolate being compatible with Xa23-containing rice.

Results: One isolate AH28 from Anhui province is compatible with CBB23. AH28 strain contains an ortholog of avrXa23, tal7b and has 17 tal genes. The 4th RVD (repeat-variable diresidue) in Tal7b are missed and the 5th and 8th RVDs changed from NG and NS to NS and S*, respectively. These alternations made Tal7b unable to bind to the EBE of Xa23 promoter to activate the expression of Xa23 in rice. The ectopic expression of tal7b in a tal-free mutant PH of PXO99^A did not alter the virulence of the strain PH, whereas avrXa23 made AH28 from compatibility to incompatibility with Xa23 rice.

Conclusion: Best to our knowledge, this is the first insight of a naturally-emerging Xoo isolate that overcomes the broad-spectrum resistance of Xa23 by the variable AvrXa23-like TALE Tal7b. The RVD alteration in AvrXa23 may be a common strategy for the pathogen evolution to avoid being "trapped" by the executor R gene.

Keywords: AvrXa23; Resistance; Rice; TALEs; Xa23; Xanthomonas oryzae pv. oryzae.

Publication types

Research Support, Non-U.S. Gov't

MeSH terms

Gene Expression Regulation, Plant
Oryza* / genetics
Oryza* / metabolism
Plant Diseases / genetics
Plant Diseases / microbiology
Transcription Activator-Like Effectors / genetics
Transcription Activator-Like Effectors / metabolism

Substances

Transcription Activator-Like Effectors

Supplementary concepts

Xanthomonas oryzae